Ore Textures

Paleolake sediments in the Northern Awash Valley, Ethiopia, can help us understand how the morphology of pyrite might be used as an environmental indicator. With the advantage of an intact mineralogical record in the ~3 million year old Hadar Formation, the Hominin Sites and Paleolakes Drilling Project (HSPDP) obtained two ~250m thick sediment cores -NAO and NAW -located ~3 kilometers in proximity to each other. In NAW, pyrite and gypsum occurred at irregular intervals while NAO only showed abundant gypsum. NAW contains pyrite in the form of framboidal and euhedral crystals. The morphology of pyrite gives insight on the effects of later rates of oxidation. Based on literature from the deep sea, framboidal pyrite suggests rapid Fereduction and pyrite precipitation, whereas euhedral pyrite crystals suggest slower reduction and precipitation rates. Through scanning electron microscopy (SEM) imaging and energydispersive X-ray spectroscopy (EDS) of samples throughout NAW, we analyzed the framboidal and euhedral crystals in pyrite. We found peaks in iron, sulfur, calcium, and carbon indicating the presence of pyrite and gypsum in select samples. Additionally, calcite is present which may have formed due to alteration of other minerals. In these samples, gypsum likely precipitated in oxidizing waters consuming sulfate produced by pyrite oxidation. Samples containing framboidal pyrite suggest an increased rate of pyrite formation toward the bottom of the core. Euhedral crystals were present toward the top of the core indicating a dwindling amount of pyrite being precipitated with time. This suggests that an environmental shift occurred that favored slower precipitation rates. The oxygenated bottom waters were most likely due to an abiotic conversion due to free oxygen. This can be a result of tectonic and/or climatic influences. Future analysis on the morphology of pyrite in NAW will provide a distinct resolution as to why there are differing amounts of pyrite in NAO and NAW.

Framboidal pyrite is common in marine sediments and organic matter-bearing sedimentary rocks. It has also been reported in many 'sediment-hosted ore deposits', such as shale-hosted massive sulfide (SHMS) or clastic-dominated Zn-Pb deposits, volcanogenic massive sulfides (VMS), Irish-type Zn-Pb, sediment-hosted stratabound copper (SSC), and sandstone-hosted Pb-Zn and U, as well as in coal deposits, whereas it is absent or rare in some others (e.g., Mississippi Valley Type, MVT). Spherulitic pyrites are more common in Cambrian pyrite-rich SHMS Zn-Pb deposits, hosted in organic matter-rich black shales and siltstones. Framboid textures can be observed in other minerals as well, such as Koushk, Zarigan, Hossein-Abad, Eastern Haft-Savaran, and Ab-Bagh ore deposits, which is consistent with the geochemical proxies of the host rocks.

This paper presents an automatic system for mineralogical and textural characterization of iron ores based on digital microscopy and image analysis. It employs a motorized and computer-controlled reflected light microscope in a correlative approach that combines bright field and circular polarization modes. Mosaic images covering large areas of polished sections are acquired to image thousands of particles. Different classifiers discriminate compact and non-compact hematite, polycrystalline and monocrystalline particles, and identify particles as granular, lamellar, and lobular. The entire process is automatic and produces a full pdf report containing typical images and the quantification of mineral and textural phases.

Ten (10) Cretaceous oil sands from different localities around the world were studied with the aim of reporting the common occurrence of authigenic pyrite crystals in them. The observed pyrite crystals (both framboid and euhedral) are restricted to the pore spaces of the studied oil sands, in close association with biodegraded oils and other authigenic minerals. Diagenetic processes in one of the studied samples triggered the transformation of framboidal pyrite crystals to octahedral pyrite crystals. This study demonstrates that geological conditions/ processes that lead to the formation of authigenic pyrite crystals in sandstones are those that favour biodegradation. Potentially, these conditions include occurrence at shallow depths (< 2000 m), moderate reservoir temperatures that can support microbial life (temperature < 80° C), availability of microorganisms that are capable of degrading oils in the reservoir, nutrient availability (e.g., iron, nitrogen, potassium, and phosphorus), and oil volume in the reservoir. Studied framboidal pyrite crystals were observed to occur within confined spaces. The oils (organic matter) associated with the studied samples are believed to have played an important role of providing the source of spherule moulds for framboid pseudomorphs and aided the stabilization of the gel in which the framboid crystals were protected. TIC fragmentograms of the saturate fractions of the oils extracted from the studied oil sands show progressive depletion of chromatographically resolved hydrocarbons (e.g. n-alkanes, acyclic isoprenoid alkanes; alkyl benzenes, naphthalenes and phenanthrenes) relative to the unresolved hydrocarbon mixture, forming unresolved complex mixture (UCM) humps, consistent with oils that have undergone biodegradation.

Burial of large quantities of magnetite (Fe(II)Fe(III)2O4) in iron formations (IFs) likely contributed to the protracted oxidation of Earth’s surface during the Precambrian Eons. Magnetite can form through a diversity of biological and abiotic pathways and its preservation in IFs may thus be variably interpreted as the result of some combination of these processes. Such interpretations thus give rise to divergent pictures of the Precambrian Earth system and models for its evolution through time. New knowledge on the contribution of specific magnetite formation pathways is, therefore, needed to accurately tether our conceptual and numerical models to the geologic record. To constrain pathways of magnetite formation under ferruginous conditions, we conducted geochemical and multi-method microspectroscopic analyses on particles obtained from the water columns and sediments of ferruginous lakes Matano and Towuti, in Indonesia. We find that biologically reactive Fe(III) mineral phases ar...

The Lower to Middle Ordovician Tøyen Shale in southern Sweden, a biostratigraphically well-dated siliciclastic mudstone unit, shows 18 distinct authigenic cements that include sulfides, carbonates, silicates, clays, and phosphates. Marcasite, sphalerite, galena, and six texturally distinct types of pyrite characterize the sulfides whereas only one type of dolomite and three different generations of calcite are observed in this unit. Quartz, phosphate, and organic matter occur as only one generation each. Authigenic clay minerals are represented by chlorite and kaolinite. The paragenetic sequence of cements is subdivided into the two pre-burial carbonates, succeeded by ten relatively early burial cements, and six late burial cements, the kaolinite being the latest of them all and potentially being of Cretaceous age. Based on textural relationships, the paragenetic sequence of alterations started with dolomite precipitation followed by calcite, and then five different generations of pyrite. All eleven other phases postdate these initial seven cements in the Tøyen Shale.

OIA (optical image analysis) has traditionally been used for reliable identification of different iron oxides and oxyhydroxides in iron ore. The automated CSIRO OIA system Mineral 4/Recognition 4 was created for rapid mineral and textural characterisation of iron ore providing identification of different minerals and different morphologies. The technique has further been applied to processed iron ore products such as iron ore sinter to determine key parameters such as porosity, different morphologies of hematite (primary and secondary), and different morphologies of SFCA (silicon ferrite of calcium and aluminium). Application of textural identification has recently been extended to coke characterisation where the software gives comprehensive characterisation of porosity, IMDC (inert material derived components), RMDC (reactive material derived components) and the boundaries between IMDC and RMDC. The software also has many unique features needed for iron ore research including characterisation of large objects like pellets and ore lumps; automated gangue (including quartz) identification; automated particle separation; multiple image set processing and on-line measurements. All these features make the Mineral 4/Recognition 4 OIA system a unique, reliable, industry/research focused tool for ore, sinter, pellet and coke characterisation.

The present study focused on overcoming the primary problem faced by any quantitative mineralogical study involving iron ore characterisation using a reflected light optical microscope; distinguishing the quartz mineral from the epoxy resin in digital images taken from mounted polished sections. Difficulties arise in this case because both phases reflect in the same colour intensity range. To overcome this problem, a digital image analysis system denominated Opt-Lib was developed. In order to evaluate the system responsivity, a characterisation study and modal and liberation analyses were performed using typical Brazilian iron ore containing quartz and the main iron oxide/hydroxide minerals: magnetite, hematite, and goethite. For the system performance evaluation, these results were compared with those generated by the scanning electron microscopy (SEM)-based Mineral Liberation Analyzer for the same sample. The results show that the main advantage of the Opt-Lib system over the SEM-based system is that it facilitates differentiation, classification, and quantification of not only the quartz mineral, but also the iron oxide/hydroxide minerals within the sample, thus providing a more precise qualitative response.

As with other radiometric "dating" methods, the U-Pb and Pb-Pb isochron methods have been questioned in the open literature, because often an excellent line of best fit between ratios obtained from a set of good cogenetic samples gives a resultant "isochron" and yields a derived "age" that has no geological meaning. At the Koongarra uranium deposit, Australia, there is ample evidence of open system behavior, or repeated migration, of U and Pb-ore textures, mineral chemistry, supergene alteration, uranium/daughter disequilibrium, and groundwater and soil geochemistry. Yet U-Th-Pb isotopic studies of the uranium ore, host rocks, and soils have produced an array of false "isochrons" that yield "ages" which are geologically meaningless. Even a claimed near-concordant U-Pb "age" of 862 Ma (million years) on one uraninite grain is identical to a false Pb-Pb isochron "age," but neither can be connected to any geological event. The open system behavior of the U-Th-Pb system is clearly the norm, as is the resultant mixing of radiogenic Pb with "common" or background Pb, even in soils in the surrounding region, apparently even up to 17 km away! Because no geologically meaningful results can be interpreted from the U-Th-Pb data at Koongarra (three uraninite grains even yield a 232 Th/ 208 Pb "age" of 0 Ma), serious questions must be asked about the validity of the fundamental/foundational basis of the U-Th-Pb "dating" method. This makes the task of creationists building their model for the geological record much easier, since claims of U-Th-Pb radiometric "dating" having "proven" the claimed great antiquity of the earth, its strata and fossils can be justifiably ignored.

The Lower to Middle Ordovician Tøyen Shale in southern Sweden, a biostratigraphically well-dated siliciclastic mudstone unit, shows 18 distinct authigenic cements that include sulfides, carbonates, silicates, clays, and phosphates. Marcasite, sphalerite, galena, and six texturally distinct types of pyrite characterize the sulfides whereas only one type of dolomite and three different generations of calcite are observed in this unit. Quartz, phosphate, and organic matter occur as only one generation each. Authigenic clay minerals are represented by chlorite and kaolinite. The paragenetic sequence of cements is subdivided into the two pre-burial carbonates, succeeded by ten relatively early burial cements, and six late burial cements, the kaolinite being the latest of them all and potentially being of Cretaceous age. Based on textural relationships, the paragenetic sequence of alterations started with dolomite precipitation followed by calcite, and then five different generations of pyrite. All eleven other phases postdate these initial seven cements in the Tøyen Shale.

With the increasing demand for minerals, the development of efficient techniques for mineral recovery is important. The application of image analysis techniques to mineral beneficiation studies is described in this paper. We carry out ore identification not pixel-by-pixel but rather by considering the average reflectance of grains. This is accomplished by first carrying out segmentation, a process in which a facet model based edge operator is used to delineate the boundaries of grains.

Otávio da Fonseca Martins Gomes Sidnei Paciornik Abstract Despite progress in Scanning Electron Microscopy (SEM) automatic instruments, these systems are not capable of performing the identification and discrimination of major iron ore minerals (hematite and magnetite). On the other hand, Reflected Light Microscopy (RLM) can easily distinguish these iron oxides by their reflectancies, but it cannot discriminate quartz and epoxy resin, which present similar color on images. Therefore, iron ore quantitative microstructural characterization is still a challenge. In the present work, a Co-Site Microscopy methodology that combines images obtained by RLM and SEM was applied to perform a quantitative characterization of an itabiritic iron ore. The so-called RLM-SEM Co-site Microscopy can discriminate phases that are not distinguishable with either RLM (epoxy resin and quartz) or SEM (hematite and magnetite) through this multimodal approach, allowing the subsequent mineralogical quantificat...

Burial of large quantities of magnetite (Fe(II)Fe(III)2O4) in iron formations (IFs) likely contributed to the protracted oxidation of Earth’s surface during the Precambrian Eons. Magnetite can form through a diversity of biological and abiotic pathways and its preservation in IFs may thus be variably interpreted as the result of some combination of these processes. Such interpretations thus give rise to divergent pictures of the Precambrian Earth system and models for its evolution through time. New knowledge on the contribution of specific magnetite formation pathways is, therefore, needed to accurately tether our conceptual and numerical models to the geologic record. To constrain pathways of magnetite formation under ferruginous conditions, we conducted geochemical and multi-method microspectroscopic analyses on particles obtained from the water columns and sediments of ferruginous lakes Matano and Towuti, in Indonesia. We find that biologically reactive Fe(III) mineral phases ar...

It has been suggested that the two morphologies of sedimentary pyrite, framboids and euhedra, may reflect two distinct pathways of pyrite formation. Framboids form indirectly via iron monosulphides, whereas euhedra form from direct precipitation from solution. A third pathway which is bridging these two forms is proposed here, namely the continuous growth from a monosulphide globule through framboids to a euhedral single crystal. It is also suggested that framboids probably occur over a range of three orders of magnitude, from the least complex microframboids through framboids to polyframboids.

Remarks on the origin of cerussite in the Upper Silesian Zn-Pb deposits, PolandCerussite, the most important oxidized lead mineral in the Upper Silesian Zn-Pb deposits, occurs in two readily distinct types: fine-grained cerussite replacing galena in-situ and macrocrystalline cerussite filling open fractures and cavities. Microscopic observations and thermodynamic considerations lead to the conclusion that galena can be oxidized to lead carbonate directly, not necessarily through an intermediate sulphate phase. Locally present iron sulphides undergoing oxidation acidify solutions and provide ferric ions which are important oxidizing agents. In such microenvironments, anglesite can preferentially form.Cerussite and galena commonly coexist together with non-oxidized zinc sulphides. It is difficult to explain such assemblages if galvanic couplings made of these two sulphides are not considered. These couplings are only formed when these two sulphides are in direct contact. In such an as...

The accumulation of metals and metalloids in diagenetic pyrite framboids is of interest because framboids can be a sink for heavy metal contaminants, a source of metals in ore deposits, and a tool to interpret paleo-ocean chemistry. In this study, we have used laser ablation-inductively coupled plasmamass spectrometry (LA-ICPMS) to analyze pyrite framboids from both the contaminated Derwent Estuary and the uncontaminated Huon Estuary in Tasmania, Australia. While the enrichment of many trace metals in the Huon Estuary followed expected trends, the trends in the Derwent were quite different. In addition to the expected high contents of Pb, Zn, and Cu in the contaminated interval it was found that several elements are not as strongly incorporated into pyrite within the contaminated zone. It is suggested that this is due to over-competition for adsorption sites on the growing iron sulfides in the contaminated zone resulting in diffusion of several elements to deeper levels in the sediments. This results in an increase of these elements in pyrite below the zone of major contamination. The LA-ICPMS technique also provided the opportunity to obtain accurate data on gold, silver, and tellurium in pyrite, something rarely achieved in sequential leach extractions due to the low concentrations of these metals observed in nature.

It has been suggested that the two morphologies of sedimentary pyrite, framboids and euhedra, may reflect two distinct pathways of pyrite formation. Framboids form indirectly via iron monosulphides, whereas euhedra form from direct precipitation from solution. A third pathway which is bridging these two forms is proposed here, namely the continuous growth from a monosulphide globule through framboids to a euhedral single crystal. It is also suggested that framboids probably occur over a range of three orders of magnitude, from the least complex microframboids through framboids to polyframboids.

Finely laminated, pyrite-and organic-rich black shales that bear a euxinic interpretation dominate the Ediacaran Lantian Formation in southern Anhui, South China. However, these black shales preserve benthic sessile algae and possible metazoans in situ, suggesting that the Lantian shelf basin may have had at least episodically oxidized bottom water during the early Ediacaran Period. Redox conditions of the fossiliferous Lantian black shales were examined by petrological analysis, pyrite framboid and ␦ 34 S measurements, and redox-sensitive trace element (RSTE) analysis. Lamina-by-lamina pyrite framboid measurements show that Lantian black shales were deposited under fluctuating redox conditions. The ␦ 34 S values of pyrites range from −20.5‰ to 2.3‰ for different laminae and display less negative values than the earliest Ediacaran black shales, supporting a return to a relatively low seawater sulfate concentration after the early Ediacaran oxidation event. Similarly, the Lantian black shale RSTE concentrations (e.g., Mo, U, and V) are low compared to previously published results from the early Ediacaran and constant from lamina to lamina, suggesting a drop in ocean wide RSTE concentrations occurring independently of frequent local redox condition changes. These frequent redox condition changes in the Lantian shelf basin may have facilitated the productivity and preservation of macroscopic Lantian biota.

Gold in the volcanogenic massive sulfide ores at Trout Lake, FIin Flon, Manitoba occurs mainly as a Au-Ag-Hg alloy, but is also present in minor amounts as &quot;invisible&quot; gold in pyrite and arsenopyrite. Two textural types of the alloy are defined: (l) inclusions, interstitial material and fracture fillings in, and coatings on, pyrite grains, and (2) anastomosing masses (s5 mm) along the folded contact between larninae of massive chalcopyrite and chlorite schist. The median grain-size of the Au-Ag-Hg alloy is ll pm, with 75Vo finer than 2l pm, The average composition (wt.9o) of the mineral is 49.290 Ag, 38.790 Au and 1l.OVo Hg, and the ranges are 17.3 to 76.5n/o Ag, 1.62 to 79.9V0 Au, and 1.29 to 30.9r/o Hg. The compositional variation reflects extensive solid-solution within the extrapolated stability field for the a-phase in the system Ag-Au-Hg. Highcontrast back-scattered electron photographs reveal systematic zoning, and a general sequence of crystallization of increasing...

Pyrite particles, having framboidal/altered texture, are known to significantly affect pulp chemistry and adversely affect flotation performance. Therefore, the main objectives of this study were to demonstrate influence of pyrite mineralogy on the flotation of copper (sulphidic) ores and develop alternative conditions to improve the performance. Two copper ore samples (Ore A and Ore B) having different textural/modal mineralogy and flotation characteristics were taken from different zones of the same ore deposit. Ore B contained framboidal pyrite and altered pyrite/marcasite, which is considered the main reason for the low flotation performance in both copper and pyrite flotation sections of the process plant. Flotation tests were conducted under different conditions using the two ore samples and a 50:50 blend. The results showed that Ore A could be concentrated under the base conditions, as applied in the existing flotation plant. On the other hand, Ore B did not respond to the ba...

Iron oxides are chemical complexes which occur naturally, comprising iron and oxygen. Here, together, 16 types of iron oxides and oxyhydroxides have been identified. These two components of oxides are widely spread naturally. They are vital to humans and useful in most geological and biological activities. In addition, they are useful as pigments and catalyst in industries and hemoglobin in blood circulation. The interplay and conversion of these components from one form to another are essentially controlled by bacterial species. These contain 70 and 72% iron, respectively. Furthermore, iron ores are classified in terms of occurrence. Banded iron formation (BIF) comprises 15% iron, comprising minerals of iron that are bedded besides silica. Beneficiation processes of iron ore generate dust in the atmosphere, acid mine drainage in the ecosystem and metallic iron for steelmaking. Beneficiation process requires dissolution of minerals surrounding the ore and the release of metals and c...

Iron oxides are chemical complexes which occur naturally, comprising iron and oxygen. Here, together, 16 types of iron oxides and oxyhydroxides have been identified. These two components of oxides are widely spread naturally. They are vital to humans and useful in most geological and biological activities. In addition, they are useful as pigments and catalyst in industries and hemoglobin in blood circulation. The interplay and conversion of these components from one form to another are essentially controlled by bacterial species. These contain 70 and 72% iron, respectively. Furthermore, iron ores are classified in terms of occurrence. Banded iron formation (BIF) comprises 15% iron, comprising minerals of iron that are bedded besides silica. Beneficiation processes of iron ore generate dust in the atmosphere, acid mine drainage in the ecosystem and metallic iron for steelmaking. Beneficiation process requires dissolution of minerals surrounding the ore and the release of metals and cement matrix into water courses. These generates acid leading to acid mine drainage. Therefore, there is a need for impact assessment of the environment in the planned beneficiation cycle. Sustainable beneficiation must be done to reduce impact on the natural, social or economic environment.

Iron ore pellets are made from refined and ground ore that is balled into spheroids and then heat treated. Pellet properties are measured through standardized physical, chemical and metallurgical tests to guarantee a high quality end product. However to better understand the oxidation and sintering of iron ore pellets one has to study the microstructures. This paper provides a proof of concept that optical microscopy combined with image analysis methods can be used to quantitatively measure phase distribution and degree of sintering in iron ore pellets.

Miocenski vulkanoklastiti u sjeverozapadnoj Hrvtaskoj zastupljeni su razlicitim varijetetima kiselih do neutralnih “tufova” i tufita. Modalni sastav vecine stijena izmijenjen je alteracijskim procesima, pa je vulkansko staklo bitan sastijak samo u tufovima Kalnika, a u svim ostalim stijenama determinirani su minerali glina i zeolit. Rezultati diskriminantne statisticke analize ukazuju na egersko-egenbursku starost svih analiziranih stijena osim badenskih bentonita Poljanske Luke. Sadržaj mikroelemenata u diferenciranim stijenama ukazuje na magmatizam vezan uz zavrsnu fazu subdukcije odnosno kolizije.

Remarks on the origin of cerussite in the Upper Silesian Zn-Pb deposits, PolandCerussite, the most important oxidized lead mineral in the Upper Silesian Zn-Pb deposits, occurs in two readily distinct types: fine-grained cerussite replacing galena in-situ and macrocrystalline cerussite filling open fractures and cavities. Microscopic observations and thermodynamic considerations lead to the conclusion that galena can be oxidized to lead carbonate directly, not necessarily through an intermediate sulphate phase. Locally present iron sulphides undergoing oxidation acidify solutions and provide ferric ions which are important oxidizing agents. In such microenvironments, anglesite can preferentially form.Cerussite and galena commonly coexist together with non-oxidized zinc sulphides. It is difficult to explain such assemblages if galvanic couplings made of these two sulphides are not considered. These couplings are only formed when these two sulphides are in direct contact. In such an as...

Solid and colloidal iron oxides are commonly involved in early diagenesis. More readily available soluble Fe(III) should accelerate the cycling of iron (Fe) and sulfur (S) in sediments. Experiments with synthetic solutions (Taillefert et al. 2000) showed that soluble Fe(III) (i.e., Ͻ 50 nm diameter) reacts at a mercury voltammetric electrode at circumneutral pH if it is complexed by an organic ligand. The reactivity of soluble organic-Fe(III) with sulfide is greatly increased compared to its solid equivalent (e.g., amorphous hydrous iron oxides or goethite). We report here data from two different creeks of the Hackensack Meadowlands District (New Jersey) collected with solid state Au/Hg voltammetric microelectrodes and other conventional techniques, which confirm the existence of soluble organic-Fe(III) in sediments and its interaction with sulfide. Chemical profiles in these two anoxic sediments show the interaction between iron and sulfur during early diagenesis. Soluble organic-Fe(III) and Fe(II) are dominant in a creek where sulfide is negligible. This dominance suggests that the reductive dissolution of iron oxides goes through the dissolution of solid Fe(III), then reduction to Fe(II), or that soluble organic-Fe(III) is formed by chemical or microbial oxidation of organic-Fe(II) complexes. In a creek sediment where sulfide occurs in significant concentration, the reductive dissolution of Fe(III) is followed by formation of FeS (aq) , which further precipitates. Dissolved sulfide may influence the fate of soluble organic-Fe(III), but the pH may be the key variable behind this process. The high reactivity of soluble organic-Fe(III) and its mobility may result in the shifting of local reactions, at depths where other electron acceptors are used. These data also suggest that estuarine and coastal sediments may not always be at steady state.

Solid and colloidal iron oxides are commonly involved in early diagenesis. More readily available soluble Fe(III) should accelerate the cycling of iron (Fe) and sulfur (S) in sediments. Experiments with synthetic solutions (Taillefert et al. 2000) showed that soluble Fe(III) (i.e., Ͻ 50 nm diameter) reacts at a mercury voltammetric electrode at circumneutral pH if it is complexed by an organic ligand. The reactivity of soluble organic-Fe(III) with sulfide is greatly increased compared to its solid equivalent (e.g., amorphous hydrous iron oxides or goethite). We report here data from two different creeks of the Hackensack Meadowlands District (New Jersey) collected with solid state Au/Hg voltammetric microelectrodes and other conventional techniques, which confirm the existence of soluble organic-Fe(III) in sediments and its interaction with sulfide. Chemical profiles in these two anoxic sediments show the interaction between iron and sulfur during early diagenesis. Soluble organic-Fe(III) and Fe(II) are dominant in a creek where sulfide is negligible. This dominance suggests that the reductive dissolution of iron oxides goes through the dissolution of solid Fe(III), then reduction to Fe(II), or that soluble organic-Fe(III) is formed by chemical or microbial oxidation of organic-Fe(II) complexes. In a creek sediment where sulfide occurs in significant concentration, the reductive dissolution of Fe(III) is followed by formation of FeS (aq) , which further precipitates. Dissolved sulfide may influence the fate of soluble organic-Fe(III), but the pH may be the key variable behind this process. The high reactivity of soluble organic-Fe(III) and its mobility may result in the shifting of local reactions, at depths where other electron acceptors are used. These data also suggest that estuarine and coastal sediments may not always be at steady state.

Ten (10) Cretaceous oil sands from different localities around the world were studied with the aim of reporting the common occurrence of authigenic pyrite crystals in them. The observed pyrite crystals (both framboid and euhedral) are restricted to the pore spaces of the studied oil sands, in close association with biodegraded oils and other authigenic minerals. Diagenetic processes in one of the studied samples triggered the transformation of framboidal pyrite crystals to octahedral pyrite crystals. This study demonstrates that geological conditions/ processes that lead to the formation of authigenic pyrite crystals in sandstones are those that favour biodegradation. Potentially, these conditions include occurrence at shallow depths (< 2000 m), moderate reservoir temperatures that can support microbial life (temperature < 80° C), availability of microorganisms that are capable of degrading oils in the reservoir, nutrient availability (e.g., iron, nitrogen, potassium, and phosphorus), and oil volume in the reservoir. Studied framboidal pyrite crystals were observed to occur within confined spaces. The oils (organic matter) associated with the studied samples are believed to have played an important role of providing the source of spherule moulds for framboid pseudomorphs and aided the stabilization of the gel in which the framboid crystals were protected. TIC fragmentograms of the saturate fractions of the oils extracted from the studied oil sands show progressive depletion of chromatographically resolved hydrocarbons (e.g. n-alkanes, acyclic isoprenoid alkanes; alkyl benzenes, naphthalenes and phenanthrenes) relative to the unresolved hydrocarbon mixture, forming unresolved complex mixture (UCM) humps, consistent with oils that have undergone biodegradation.

Remarks on the origin of cerussite in the Upper Silesian Zn-Pb deposits, PolandCerussite, the most important oxidized lead mineral in the Upper Silesian Zn-Pb deposits, occurs in two readily distinct types: fine-grained cerussite replacing galena in-situ and macrocrystalline cerussite filling open fractures and cavities. Microscopic observations and thermodynamic considerations lead to the conclusion that galena can be oxidized to lead carbonate directly, not necessarily through an intermediate sulphate phase. Locally present iron sulphides undergoing oxidation acidify solutions and provide ferric ions which are important oxidizing agents. In such microenvironments, anglesite can preferentially form.Cerussite and galena commonly coexist together with non-oxidized zinc sulphides. It is difficult to explain such assemblages if galvanic couplings made of these two sulphides are not considered. These couplings are only formed when these two sulphides are in direct contact. In such an as...

matic rocks (albitite, microclinite, altered mafic rocks), and (3) pegmatites, silexites, and hydrother mal veins. BRIEF CHARACTERIZATION OF SILEXITES Silexite (quartzolite) is a rock primarily composed of quartz (>60 vol %) representing a pegmatitic or hydrothermal end member of granitic magma frac tionation. The quartz to feldspar ratio in silexites does not fall below 9 : 1. The other major rock forming constituents are dark colored (amphibole, pyroxene, mica) and ore (magnetite, ilmenite) minerals. This rock attracted attention owing to the discovery of the large Jabal Hamra rare metal deposit in the Arabian Shield, which is hosted within a silexite related to alkali granite (Drysdall et al., 1984). As concerns the Kola alkali granites, the term silexite was introduced by Bel'kov et al. (1988) for late magmatic rocks, which occupy a transitional position between early high temperature orthomagmatic granites proper and fluid magmatic rocks like schlieren pegmatites, on the one hand, and mesothermal hydrothermal rocks

Gold in the volcanogenic massive sulfide ores at Trout Lake, FIin Flon, Manitoba occurs mainly as a Au-Ag-Hg alloy, but is also present in minor amounts as "invisible" gold in pyrite and arsenopyrite. Two textural types of the alloy are defined: (l) inclusions, interstitial material and fracture fillings in, and coatings on, pyrite grains, and (2) anastomosing masses (s5 mm) along the folded contact between larninae of massive chalcopyrite and chlorite schist. The median grain-size of the Au-Ag-Hg alloy is ll pm, with 75Vo finer than 2l pm, The average composition (wt.9o) of the mineral is 49.290 Ag, 38.790 Au and 1l.OVo Hg, and the ranges are 17.3 to 76.5n/o Ag, 1.62 to 79.9V0 Au, and 1.29 to 30.9r/o Hg. The compositional variation reflects extensive solid-solution within the extrapolated stability field for the a-phase in the system Ag-Au-Hg. Highcontrast back-scattered electron photographs reveal systematic zoning, and a general sequence of crystallization of increasingly Ag-rich compositions. This sequence reflects the increased activity of bisulfide complexes of Ag compared to those ofAu and Hg in the evolved pore-fluids during retrograde metamorphism, and its episodic diffusion into earlier formed, more intermediate compositions, under disequilibrium conditions. The average "invisible" gold content, determined by SIMS analysis, is 0.72 ppm in arsenic-poor pyrite, and 30.2 ppm in arsenopyite. Approximately 9390 of the Au in the ore occurs as Au-Ag-Hg aUoy, with 6 and lVo as "invisible" gold in pyrite and arsenopyrite, respectively.

Cast iron presents graphite particles of different shapes that directly affect its thermo-mechanical properties [1]. Fracture toughness and ductility depend strongly on the shape of the graphite particles. Particles with nodular shapes improve these properties while more elongated particles or with irregular contours are detrimental due to stress concentration points [2]. Thus, cast iron is classified according to the shapes of its graphite particles. The ISO-945 standard presents six classes to characterize the different shapes of graphite particles. Fig. 1 shows the six synthetic reference images that represent these classes.

The recognition of hematite grains is an intermediate task that aids the texture characterization of iron ores. Hematite is a strongly anisotropic mineral. Thus, the combined use of a polarizer and an analyzer in reflected light microscopy (RLM) can be used to obtain images that present sufficient contrast to differentiate grains. The present work proposes a methodology for recognizing hematite grains in images obtained with RLM. Three images per field are acquired in different conditions: without polarization in common bright field arrangement; and with polarization under two symmetrical polarizer/analyzer angles. These images are automatically registered. Then, the hematite grains are recognized through a modified region growing segmentation method based on reflectance and textural information. An optimal value for the polarization angle was determined. The results are promising. The vast majority of grains was correctly recognized. The automatically segmented images were compared to edited versions in which all crystals were correctly discriminated. A statistical comparison of crystal size and shape showed no statistical differences, to within 99% confidence, between automatic and edited segmentation results.

Zn(II) and Pb(II) from Nigerian sphalerite and galena ores were bioleached by a mixed culture of acidophilic bacteria. The influences of pH and ferric ion on the bioleaching rates of sphalerite and galena were examined. The result shows that pH 2.1 and 2.7 are favourable for the leaching of Zn(II) and Pb(II) from sphalerite and galena, respectively. It was observed that the use of agarose-simulated media caused cells to excrete exopolymers containing ferric ions which enhanced oxidation. The oxidation equilibrium for sphalerite and galena took 3 and 4 d, respectively. About 38.3% sphalerite and 34.2% galena were leached within 1 d and approximately 92.0% Zn(II) and 89.0% Pb(II) were recovered in 5 d, respectively. The unleached residual products were examined by X-ray diffraction for sphalerite, revealing the presence of elemental sulphur(S), zinc sulphate (ZnSO 4) and few traces of calcium aluminate (Ca 3 Al 2 O 6). The XRD pattern also indicates the presence of elemental sulphur (S), lead sulphate (PbSO 4) and few traces of itoite [Pb(S,Ge)(O,OH) 4 ] and cobalt lead silicate [Pb 8 Co(Si 2 O 7) 3 ] in the unleached galena ore.

Sulphide, sulphite, thiosulphate, sulphate and total sulphur were analyzed in batch leaching tests and in a percolation test to study sulphur leaching from oil shale semicoke. The results showed that thiosulphate is the major sulphur species in the semicoke leachate in the conditions of usual disposal practice.

In recent years, leaf image recognition and classification has become one of the most important subjects in computer vision. Many approaches have been proposed to recognise and classify leaf images relying on features extraction and selection algorithms. In this paper, a concept of distinctive hybrid descriptor is proposed consisting of both global and local features. HSV Colour histogram (HSV-CH) is extracted from leaf images as the global features, whereas Local Binary Pattern after two level wavelet decomposition (WavLBP) is extracted to represent the local characteristics of leaf images. A hybrid method, namely "Hybrid Descriptor" (HD), is then proposed considering both the global and local features. The proposed method has been empirically evaluated using four data sets of leaf images with 256×256 pixels. Experimental results indicate that the performance of proposed method is promisingthe HD outperformed typical leaf image recognising approaches as baseline models in experiments. The presented work makes clear, significant contribution to knowledge advancement in leaf recognition and image classification.

The accumulation of metals and metalloids in diagenetic pyrite framboids is of interest because framboids can be a sink for heavy metal contaminants, a source of metals in ore deposits, and a tool to interpret paleo-ocean chemistry. In this study, we have used laser ablation-inductively coupled plasmamass spectrometry (LA-ICPMS) to analyze pyrite framboids from both the contaminated Derwent Estuary and the uncontaminated Huon Estuary in Tasmania, Australia. While the enrichment of many trace metals in the Huon Estuary followed expected trends, the trends in the Derwent were quite different. In addition to the expected high contents of Pb, Zn, and Cu in the contaminated interval it was found that several elements are not as strongly incorporated into pyrite within the contaminated zone. It is suggested that this is due to over-competition for adsorption sites on the growing iron sulfides in the contaminated zone resulting in diffusion of several elements to deeper levels in the sediments. This results in an increase of these elements in pyrite below the zone of major contamination. The LA-ICPMS technique also provided the opportunity to obtain accurate data on gold, silver, and tellurium in pyrite, something rarely achieved in sequential leach extractions due to the low concentrations of these metals observed in nature.

Fassinaite, ideally Pb 2 2+ (S 2 O 3 )(CO 3 ), is a new mineral from the Trentini mine, Mount Naro, Vicenza Province, Veneto, Italy (holotype locality). It is also reported from the Erasmus adit, Schwarzleo District, Leogang, Salzburg, Austria and the Friedrich-Christian mine, Schapbach, Black Forest, Baden-Württemberg, Germany (cotype localities). At the Italian type locality it occurs as acicular [010], colourless crystals up to 200 mm long, closely associated with galena, quartz and anglesite. At the Austrian cotype locality it is associated with cerussite, rare sulphur and very rare phosgenite. At the German cotype locality anglesite is the only associated phase. Fassinaite crystals commonly have flat chisel-shaped terminations. They are transparent with vitreous to adamantine lustre and a white streak. Fassinaite is brittle with an irregular fracture and no discernible cleavage; the estimated Mohs hardness is 1ÝÀ2. The calculated density for the type material is 6.084 g cm À3 (on the basis of the empirical formula), whereas the X-ray density is 5.947 g cm À3 . In common with other natural lead thiosulphates (i.e. sidpietersite and steverustite) fassinaite has intense internal reflections, which do not allow satisfactory optical data to be collected; the crystals are length-slow and have very high birefringence. The mineral is not fluorescent.

In Viet Nam, non-sulfide zinc ore in the Cho Dien deposit has been exploited for a long time. Up to the present, zinc ore remains the major exploited ore in Cho Dien. There are numerous studies of Pb-Zn ore in Cho Dien. However, most of the studies have dedicated only to description of mineralogical and chemical composition of Pb-Zn ore. There has been no publication on this non-sulfide zinc ore. Based on the mineralogical studies , the content of Pb and Zn in groundwater determined by reflective microscope, SEM, EPMA and ICP-MS methods, the study explained the formation of secondary non-sulfide zinc ore in the Cho Dien deposit. Strong weathering process makes the upper part of ore bodies completely oxidized. Difference in geochemical behavior of lead (Pb) and zinc (Zn) in the oxidation process of Pb-Zn ore is the reason to form non-sulfide zinc ore in the Cho Dien deposit. Oxidation of primary Pb-Zn ore is mainly sphalerite, pyrite, galena minerals which creates a low pH environment and transforms of zinc from immobile (sphalerite-ZnS) to mobile (Zn 2+) and retained in solution under acid pH conditions whereas lead has the tendency to form soluble minerals (angle-site, cerussite). The acid neutralization actions of the surrounding rocks make zinc precipitate, to form secondary non-sulfide zinc minerals.

Vale (previously CVRD – Companhia Vale do Rio Doce) evaluates the microstructure of sinters in order to understand their characteristics and behaviour in the agglomeration process, and the correlation with conventional quality parameters. Efforts on image analysis development are in progress between Vale and PUC-Rio in order to improve both the qualitative and quantitative evaluation of a representative portion of material. In the present work, digital microscopy techniques were developed allowing this kind of assessment. Employing a motorised and computer controlled optical microscope, low magnification mosaic images covering complete sinter samples were automatically obtained. The mosaics provide a powerful qualitative overview of the whole sample while allowing low resolution quantitative evaluation of the major phases. In addition, quantitative results for phase fractions were compared for the same sample regions at three magnifications (5×, 10× and 20× objective lenses). A single field (1 × 1) at the lowest magnification corresponds to mosaics of 2 × 2 and 4 × 4 images at the higher magnifications. The automated system allows perfect registration between the mosaics and the single image. Changes in phase discrimination were evaluated as a function of optical resolution, and phase fractions obtained by interactive segmentation of the image histograms were compared. While finer dark phases, eg silicates, were only visible with the best optical resolution, coarser phases such as haematite and pores were measured at all resolutions. For haematite, magnetite, ferrite and pores, the largest relative error in area fraction, between the images obtained with the 5× and 20× lenses, was 12 per cent. The results for silicate were less accurate with a relative error of 44 per cent. The results indicate that digital microscopy provides a flexible method for qualitative and quantitative evaluation of these materials.

Non-sulfide zinc ore in the Cho Dien deposit has been exploited for a long time and remains the major exploited ore in Cho Dien. There are numerous studies of Cho Dien Pb-Zn ore,however, many of the studies have dedicated to description of mineralogical and chemical compositions. Built on the mineralogical studies and the content of Pb and Zn in groundwater determined by reflective microscope, SEM, EPMA and ICP-MS methods, the study explained the formation of secondary non-sulfide zinc ore in the Cho Dien deposit. The upper part of ore bodies was weathered and completely oxidized. Difference in geochemical behavior of lead (Pb) and zinc (Zn) in the oxidation process of Pb-Zn ore led to the formation of non-sulfide zinc ore in the Cho Dien deposit. Oxidation of primary Pb-Zn ore minerals such as sphalerite, pyrite and galena creates a low pH environment and transforms zinc from immobile (sphalerite-ZnS) to mobile (Zn 2+) and is retained in solution under low(acidic) pH conditions; whereas lead has the tendency to form soluble minerals (anglesite, cerussite). The acid neutralization of the surrounding rockcauseszinc to precipitateto form secondary non-sulfide zinc minerals.

Oxidation of iron sulfide minerals (mainly pyrite and pyrrhotite) occurs in mine waste and other mining environments which is a natural process associated to weathering reactions and produced by waste spillage due to eolic or pluvial dispersion. Iron sulfides environmental weathering results in secondary sulfur and iron (III) oxyhydroxides (IOH's) formation whose mineralogical transformation affects iron sulfides reactivity inducing sulfides passivation and/or enhanced mineral reactivity. Review reports considering IOH's dynamic behavior are sparse and barely found. In this review work, authors update iron sulfides weathering and IOH's relationship and also include some original and experimental data, aiming to establish main IOH's occurrence and stability during iron sulfides weathering under environmental conditions in mining environments.

The African portion of Southwest Gondwana is endowed with an enormous wealth of mineral resources. Certain types of ore deposits occur in metallotects that share common geological and metallogenetic features. These can include host rocks, the age and mode of origin of the mineralisation, the commodity elements or minerals, and the geodynamic significance of formation.
The present chapter describes metallotects that are significant for the regional and supra-regional geological and plate tectonic evolution and bear metallogenetically and economically important mineral resources. The size of metallotects or individual deposits described here is variable from the world-class Cu-Co-resource of the Central African Copperbelt to economically insignificant but metallogenetically relevant tin deposits in the Cape Peninsula of South Africa. The chapter includes settings such as Late Mesoproterozoic extensional, volcano-sedimentary continental to shallow marine basins with the deposits contained therein. The chapter describes also the Neoproterozoic, more continuous, deeper water and locally sea floor-basalt-bearing Damara Belt with its metabasalt-hosted massive sulphide Cu-Zn deposits and the sediment-hosted Pb-Zn deposits along the basin margins. However, for some of the metallotects, the age of the mineralisation is epigenetic and unrelated to the period of the deposition of the host rocks. The comparatively poorly exposed, studied and explored West Congo Belt is also included, particularly since it bears a lithologically, structurally and metallogenetically strong resemblance to the Damara Belt further south.
Orthomagmatic copper sulphide deposits, such as the ones of the Mesoproterozoic Okiep District, represent a comparatively small but historically and metallogenetically important metallotect in the Northern Cape Province of South Africa. In contrast, ore deposits related to highly fractionated felsic to exotic magmatic rocks have formed during the late to post-orogenic stages in collisional plate tectonic settings.

distribution. They occupy a definite stratigraphic level in the geological section of the deposit. On the basis of new paleontological data this level is assign to Reinhardtites anthophorus nannoplankton Subzone (CC 22c). Concretions from different parts of the deposit are characterized by a concentric-banded structure, as well as by the same content of ore minerals. Thin lamination of hosting tuffs arch-like overwrap the concretions. Formation of the concretions presumably occurred contemporaneously with syngenetic ore bodies, as well as with hosting rocks, before a complete compaction of these rocks.